The present invention relates to a method and apparatus for measuring flow velocity of a fluid. The invention is particularly useful in various types of systems including: a system for measuring heat flow; an anemometer for measuring wind velocity and direction; and a wind tunnel for measuring wind velocity. The invention is therefore described below with respect to the above applications, but it will be appreciated that the invention can advantageously be used in other applications as well.
There are many situations wherein it is necessary or desirable, e.g., for cost allocation purposes or for billing purposes, to measure heat flow, i.e., heat taken from or added to a system. Examples of the above include hot-water heating systems, air conditioning systems, heat exchangers, waste-heat recovery units, de-super heaters, and solar heating systems. In many cases such as in heating and air conditioning systems, the electrical energy consumed in generating the heat added to the working fluid, or in extracting the heat from the working fluid, cannot be conveniently distinguished for cost-allocation or billing purposes from the electrical energy consumed for other uses, e.g., for lighting, operating machines, etc. There is therefore a need for a simple, efficient and inexpensive system for measuring heat flow directly.
Another field in which the present invention is particularly useful is in anemometers for measuring the velocity and direction of the wind. The anemometers commonly used today for this purpose generally include mechanically moving parts which are prone to errors, particularly during long periods of operation, because of soiling by dust transported with the air and failure of electric components by aging. Similar drawbacks are involved in measuring the velocity of the wind in wind tunnels. Therefore, there is also a need for a simple, efficient and inexpensive system for measuring wind velocity and/or wind direction in an anemometer or wind tunnel.